1. Field of the invention
The present invention relates to an impact energy absorption structure for a motor vehicle and particularly to an impact energy absorption structure for absorbing an impact energy when a vehicle has a head-on collision.
2. Prior Arts
The body front structure is primarily composed of left and right front frames connected with the inner side of a font wheel apron and having a closed section structure in the longitudinal direction of the vehicle, and a front bumper connected with each front end of the left and right front frames through a bumper stay. When a vehicle equipped with an air bag system has a head-on collision, first the front bumper is collapsed and then an impact load is inputted to the left and right front frames respectively through a bumper beam and a bumper stay. Then, the impact load is inputted to the left and right frames respectively and the impact energy is absorbed by a buckling deformation of the front frames. An air bag is operated when the impact load is inputted to the front frames. One example of this technology is disclosed in Japanese Utility Model Application Laid-open No. Jitsu-Kai-Hei 6-18165.
In case of the vehicle equipped with an airbag system, it is necessary to make a tuning of impact sensing in order to prevent a crash sensor from sensing an impact at the event of a light collision. For example, in the prior art shown in FIG. 5, the tuning is made by use of a bumper st ay connected to the front end of a front frame. That is, when an impact load is inputted, the impact energy is absorbed temporarily by the collapse of the bumper stay. In FIG. 5, "a" denotes a front frame, "b" denotes a front bumper, "c" denotes a bumper beam, "d" denotes a bumper stay, "e" denotes a toe board, "f" denotes a floor tunnel and "g" denotes a crash sensor. Generally, the front frame "a" is connected by butt welding at the rear end thereof with the toe board "e" and the crash sensor "g" is installed at a portion reinforced by a cross member (not shown)in the floor tunnel "f".
In this case, a certain length L.sub.1 of crash stroke must be secured a t the front of the front frame "a", however, in case of vehicles having a relatively short front overhang like mini-cars and one-box cars it is difficult to establish an appropriate length of crash stroke between the front bumper and the front frame.